An aircraft with inertial reference systems can estimate aircraft navigation performance based on Actual Navigation Performance (ANP), which refers to the current navigation performance of the aircraft. The Actual Navigation Performance informs the pilot as to whether the reported position of the aircraft is within the Required Navigation Performance (RNP), the accuracy required for a given block of airspace, leg or a specific procedure.
Actual Navigation Performance can be calculated based on measurements from inertial reference systems. However, over time, the inertial reference systems can exhibit position errors due to integration drift. For instance, inertial navigation can include small errors in the measurement of acceleration and angular velocity. These errors can be integrated into progressively larger errors in velocity, which can be compounded into still greater errors in position. To compensate for these errors, navigation aid measurements can be provided by a navigation system (e.g., Global Positioning System or ground-based radio navigation aids). These measurements can be used to estimate the inertial errors and remove such errors from the calculations made by the inertial reference systems—allowing for more accurate calculations of position, velocity, and Actual Navigation Performance. However, in some circumstances (e.g., when the aircraft is on approach), navigational aid measurements may not be available to correct these inertial errors. As such, predicting aircraft navigation performance can become difficult.